Preparation of trioxane



Patented Apr. 25, 1944 y UNITED STATES PATENT OFFICE 2,347,447 PREPARATION OF TRIOXANE Joseph Frederic Walker, Lewiston, N. Y., a'ssignor to E. I. du Pont de Nemours & Company, Wilmington, Del, a corporation of Delaware No Drawing. Application April 30, 194.2, Serial No. 441,230

6 Claims. (Cl. 260-340) This invention relates to the preparation and the distillate will be at a minimum, theweight recovery of symmetrical trioxane,the cyclic fo'rmratio of formaldehyde to trioxane therein in no aldehyde trimer which is also known as alphacase exceeding 0.5. trioxymethylene. It is also directed to a new In previous methods wherein the character of and valuable azeotropic mixture of triox'ane and the distillate or the temperature at which distilwater. lation takes place are not controlled, it has fre- More particularly, the invention relates to the quently been necessary to distill four pounds or separation and recovery of trioxane (alpha-trimore of formaldehyde per pound of trioxane reoxymethylene) from aqueous mixtures containcovered. In accordance with my improved procing trioxane in association with greater or lesser 10 ess, as high as 60-70% of the distillate may comamounts of formaldehyde. This is accomplished prise the desired trioxane product. In this way by utilization of a process wherein the trioxane the cost of the distilling operation per pound of is recovered by distilling the aqueous mixture recovered s-trioxane is greatly reduced.

under carefully controlled conditions. General- Accordingly, one of the objects of this invenly the aqueous mixture will include, in addition tion is the development of an improved process to trioxane and formaldehyde, an acidic subfor isolating or recovering symmetrical trioxane stance, such as sulfuric acid. Under these con- (alpha-trioxymethylene) from aqueous solutions ditions the formaldehyde is converted to trioxane containing formaldehyde in addition to the trias will be more fully explained below. oxane, this procedure being such that but mini- I am primarily concerned with the isolation mum amounts of water and formaldehyde are of trioxane by distilling the reaction mixture distilled per pound of product. Another object of under such conditionsthat the distillate comprises this invention involves the accomplishment of a maximum percentage of the desired product. t e o e o n p p y Operating 80 that the This means that for given amounts of trloxane, composition of the distillate approaches as closethe distillate contains minimal amounts of formy as DOSSible an aZeOtrOpic miXtU-le Of Water and aldehyde and water. These results are accomtrioxane, which mixture Will, ev also plished by carrying out the distillation under erally Conta greater 185581 amounts of formcarefully controlled temperature conditions, aldehyde, the amount of formaldehyde not ex- It is appreciated in the art that symmetrical ceeding 0.5 pound per pound of trioxane. These trioxane maybe prepared from aqueous solutions d St rthe Objec of y invention Will be of formaldehyde which are acidic in reaction. In apparent r the ensuing disclosure of certain one typical process an acidic solution of formalp e e e e bodime ts the eo dehyde is utilized, which solution has a hydrogen The solution from which the trioxane is recovion concentration corresponding to that caused cred may e n containing w e f l ehy by the presence of from 0.1 to 4.0% by weight of and trioxane, also containing, in addition, other sulfuric acid. The s-trioxane is formed in the materials such as acidic catalysts. As an alteraqueous formaldehyde solution and is removed native, the solution y constitute ss ntially a therefrom by distillation, the desired product beaqueous solution of f m l hyde c ntainin n ing found in the distillate. In all previous procacidic lys th tion h vin a hy r n esses, however, no'attempt ha b d t 40 ion concentration corresponding to that caused by cure a distillate which contains a maximum the presence of from 0.1 to 4.0 pe y Weight amount of trioxane, on i h 't amounts of sulfuric acid. In the latter case, in accordance of formaldehyde and water per und of recom with well-understood principles, the trioxane is ered product are relatively n formed in situ during the operation. The concen- I have now discovered that by carefully tration of formaldehyde in the starting solution trolling the temperature at which the aqueous m y y from 30 to 0%, l h h h con nmixture of formaldehyde and trioxane (usually tldtioll Should preferably 9111 Within e range .alsocontaining various amounts of acid) is sub- 5% e most t c y e ts.

jected to distillation, it is possible to operate so The reaction medium is subje ed o dist that the percentage of trioxane in the liquid col- 50 tion under conditions such that a constant boillected in the condenser is very high. Specifically, ing mixture having a boiling point within the I have found that by carefully controlling the range 90 to 92 C. is distilled from the apparatus. distillation sothat the vapors passing over are This is preferably accomplished by employing an only those boiling within the range 90-92 0., the efficient distillation column. Where the initial amounts of water and formaldehyde present in starting material comprises an acidic solution of formaldehyde, containing a strong acidic catalyst equivalent to from 0.1 to 4.0% concentration of sulfuric acid by weight, the distillation should take place under reflux at a rate consistent with trioxane formation. Symmetrical trioxane passes over into the distillate, from which it may readily be recovered by treatment with any water-immiscible solvent.

The proportions of trioxane, formaldehyde, and

water in the distillate when aqueous solutions of formaldehyde of varying concentrations are distilled are given in the following table, This table also discloses the boiling pointyabout 913 C., and the composition of the azeotropic "mix; ture comprising 70% by weight of trioxaneand 30% by weight of water.

. The s trioxane ,may be isolated by extraction in a continuous orbatch process by means of a water-immiscible solvent. The distillate may be returned to the reaction vessel, fortified by the addition of further amounts of formaldehyde equivalent to the trioxane extracted, and subjected to redistillation under constant boiling condifigns. f I.

The product is a white crystallinesolid melting at 63 -4 C. and boiling at Ila 5 C. It is very solublein methylene chloride acetone, and chloroform, and readily solublelin carbon tetrachloride. alcohol, ether, and benzene. It isdifficultly soluble in petroleum ether. At'room temperature trioxane dissolves in Water to the extent of, about 20%. It is evident that any of the water i nmiscible solvents noted may be utilized for its extraction 'from the condensate collected in the condenser or collector in'comml'inication wlth thestlll apparatus V 'The new azeotropic canstant boiling'mixtu're'of A charge of 1014-parts of 61.4% formaldehyde solution containing 2.25% sulfuric acid was placed in aglass still pot equipped with an agitator and a packed fractionating column surmounted by a still head equipped with anadjustable bayonet condenser. The receiving apparatus wa so arranged that vapors leaving the still head would pass through'a glass chamber, containing a bimetallic thermoregulator -which controlled the electric elements supplying heat to the still pot, from which they then passed into a vessel which acted both as a receiver and condenser. This vessel, which contained trichlorobenzene, was maintained at a temperature in the range 30-l0 C. and was so constructed that the hot vapors entered below the surface of the solvent.

Distillation was carried out at such a rate that the vapors leaving the still head were in the temperature range 90-92 C. This rate was controlled by adjusting the thermoregulator and maintaining an adequate reflux ratio in the distilling column. I Upon condensing, the vapors were extracted by the trichlorobenzene. The s-trioxane formed dissolved in this solvent, whereas formaldehyde and water condensed to form aqueous formaldehyde, which floated on the top of the trichlorobenzene phase.

The trichlorobenzene extract and formaldehyde solution were removed from the receiver from time to time and fresh triohlorobenzene was added. The trichlorobenzene extract removed -Was washed with a small amountof 28% ammonia and dried with calcium chloride. (It was then placed in a still and its trioxane content isolated.

by distillation. Solvent from which the s-trioxane had thus been removed could then be reused in the process. Recovered formaldehyde was reutilized to produce further amounts of s-trioxane after fortification to 60% concentration. The yield ofs-trioxane was as based-on formaldehyde consumed. The distillate from the reactor contained approximately 0.4 gram formaldehyde per gram.

s-trioxane.

It is apparent that various changes and variations conforming to the spiritof the invention may be carried out, and such variations are'intended to be included within thescope of the appended claims.

I claim:

1. A process for separating trioxane from an aqueous mixture in which it is present with formaldehyde which comprisesdistilling said aqueous mixture under such conditions that the distillate comprises essentially only a'.low.-boiling mixture having -a boiling pointwithintherange -92 C., saiddistillate comprising trioxane and water, and an amount of formaldehyde not excee.ding,0.5 part by weight for each part of trioxane. present therein; and then separating .thetrioxanefroin the-distillate.

2. A process for separating trioxane from an aqueous mixture in whichit is present with form.- aldehyde Which. comprises distilling said aqueous mixture under such conditions that the distillate comprises essentially only a low boiling. mixture having a boiling point within the range 90=92.C., said distillate comprising trioxane and waterand an amount of formaldehyde not exceeding 0.5 part by weight for each part of trioxane present therein; and then treating said distillate witha solvent for trioxane which isimmiscible'with water in order to extract said trioxane therefrom.

3. A process. for recovering trioxane which comprises distilling an aqueous solution of formaldehyde containing from 30 to 70% of formaldehyde under such conditions that only a low boiling mixture having a boiling point within the range 90 to 92 C. is distilled, said low boiling mixture comprisin water, trioxane and formal-, dehyde, the formaldehyde content thereof not exceeding 0.5 part by Weight for each part of trioxane present; and then recovering trioxane from saiddistillate.

4. A process for recovering trioxane which comprises distilling an aqueous solution of formaldehyde containing from 30 to 70% of formaldehyde under such conditions that only a low boiling mixture having a boiling point within the range 90 to 98 C. is distilled, said mixture comprising water, trioxane and formaldehyde, the formaldehyde content thereof not exceeding 0.5 part by weight for each part of trioxane present; and then treating said distillate with a solvent for trioxane which is immiscible with water in order to extract said trioxane therefrom.

5. A process for recovering trioxane which comprises distilling an aqueous solution of formaldehyde containing from 30 to 70% of formaldehyde, said solution havin a hydrogen ion concentration corresponding to that caused by the presence of 0.1 to 4.0% by weight of sulfuric acid, said distillation being carried out under such conditions that only a low boiling mixture boiling within the range 90-92 C. is distilled, said mixture comprising trioxane, water, and an amount of formaldehyde not exceeding 0.5 part by weight for each part of trioxane present; and then separating the trioxane from said distillate.

6. A process for recovering trioxane which comprises distilling an aqueous solution of formaldehyde containing from to of formaldehyde, said solution having a hydrogen ion concentration corresponding to that caused by the presence of 0.1 to 4.0% by weight of sulfuric acid, said distillation being carried out under such conditions that only a low boiling mixture boiling within the range -92 C. is distilled, said mixture comprising trioxane, water, and an amount of formaldehyde not exceeding 0.5 part by weight for each part of trioxane present; and then treating said distillate with a solvent for trioxane which is immiscible with water in order to extract said trioxane therefrom.

JOSEPH FREDERIC' WALKER.

CERTIFICATE OF CORRECTION. Patent No. 2,5u7,lm7. April 25, 19th.

JOSEPH FREDERIC WALKER.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 5,.firsL column, line 6, claim 1;, for "90 to 98 c." read --90 to 92 c.--; and that the said Letters .Patent should be read with this correction therein that the same may conform to the record of the case in. the Patent Office.

Signed and sealed this 6th day of June, A. D. 19%.

Leslie Frazer (Seal) Acting Commissioner of Patents. 

